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Delta Aquilae
	Location of δ Aquilae (circled) near the center
Observation data; Epoch J2000 Equinox J2000
Constellation	Aquila
Right ascension	19h 25m 29.90139s
Declination	+03° 06′ 53.2061″
Apparent magnitude (V)	3.365
Characteristics
Spectral type	F0 IV + K
U−B color index	+0.031
B−V color index	+0.319
R−I color index	+0.16
Variable type	δ Sct
Astrometry
Radial velocity (Rv)	−30.1 km/s
Proper motion (μ)	RA: +254.54 mas/yr ; Dec.: +82.51 mas/yr
Parallax (π)	64.41 ± 1.00 mas
Distance	50.6 ± 0.8 ly ; (15.5 ± 0.2 pc)
Absolute magnitude (MV)	2.46
Orbit
Period (P)	3.426 ± 0.006 yr
Semi-major axis (a)	0.0539 ± 0.0040″
Eccentricity (e)	0.36 ± 0.07
Inclination (i)	150 ± 11°
Longitude of the node (Ω)	337 ± 9°
Periastron epoch (T)	1,954.58 ± 0.13
Argument of periastron (ω); (secondary)	191 ± 14°
Details
δ Aql Aa
Mass	1.65 M☉
Radius	2.01±0.04 R☉
Luminosity	8.52±0.26 L☉
Surface gravity (log g)	4.03 cgs
Temperature	6,958 ± 46 K
Metallicity [Fe/H]	−0.04 dex
Rotational velocity (v sin i)	87.3 km/s
δ Aql Ab
Mass	0.67 M☉
Radius	0.61 R☉
Other designations
	Al Mizān I, δ Aql, 30 Aql, BD+02° 3879, FK5 730, GJ 760, HD 182640, HIP 95501, HR 7377, SAO 124603, NLTT 47775
Database references
SIMBAD	data

Delta Aquilae, Latinized from δ Aquilae, is a binary star system in the equatorial constellation of Aquila. It has an apparent visual magnitude of 3.4^[2] and, based upon parallax measurements, is located at a distance of about 50.6 light-years (15.5 parsecs) from Earth.^[1] It is drifting closer with a radial velocity of −30 km/s.^[6] The system is predicted to come to within 25.4 ly (7.8 pc) of the Sun in around 335,000 years.^[13]

Properties

The binary nature of this system was first reported by H. L. Alden at Yale Observatory in 1936. It is an astrometric binary where the two components orbit each other with a period of 3.422 years and an eccentricity (ovalness) of about 0.36.^[8] This is a type of binary star system where the presence of the secondary component is revealed by its gravitational perturbation of the primary. The individual components have not been resolved with a telescope.

The primary member, designated component Aa, is an aging subgiant star with a stellar classification of F0 IV,^[3] where the luminosity class of IV indicates it is in the process of exhausting the supply of hydrogen at its core and evolving into a giant star. The mass of the star is 65% greater than the Sun's^[4] and it has expanded to more than double the Sun's radius. It is radiating around 8.5 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 6,958 K,^[9] giving it the yellow-white hue of an F-type star. Delta Aquilae A is a Delta Scuti variable that exhibits variations in luminosity caused by pulsations in its outer envelope.^[5] It is spinning rapidly with a projected rotational velocity of about 87 km s⁻¹. This is a lower bound on the azimuthal velocity along the star's equator.^[11]

The secondary, component Ab, is a smaller star with about 67% of the Sun's mass and an estimated 61% of the radius of the Sun.^[4] It may be a K-type star.^[4]

Naming

This star, along with η Aql and θ Aql were Al Mizān (ألميزان), the Scale-beam.^[14] According to the catalogue of stars in the Technical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars, Al Mizān were the title for three stars: δ Aql as Al Mizān I, η Aql as l Mizān II and θ Aql as Al Mizān III.^[15] Being the westernmost star of the asterism, Jim Kaler has suggested the name Almizan Occidental.^[16]

On the other hand, Antonín Bečvář includes, with no further explanation, Deneb Okab in his catalogue,^[17] meaning the tail of eagle in Arabic; however, the star is situated in the centre of the constellation, which is usually identified with the chest, while the stars ε Aql and ζ Aql have been collectively known as Deneb al Okab by Arabian medieval astronomers,^[14] which might suggest that Bečvář's assumption was a misnomer.

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Djenubi Menkib al Nesr (منكب ألنسر ألخنوبي – mankib al-nasr al-janúbii), which was translated into Latin as Australior Humerus Vulturis, meaning the southern shoulder of the eagle.^[18]

In Chinese, 右旗 (Yòu Qí), meaning Right Flag, refers to an asterism consisting of δ Aquilae, μ Aquilae, σ Aquilae, ν Aquilae, ι Aquilae, 42 Aquilae, HD 184701, κ Aquilae and 56 Aquilae.^[19] Consequently, the Chinese name for δ Aquilae itself is 右旗三 (Yòu Qí sān, English: the Third Star of Right Flag).^[20]

This star, together with η Aql, θ Aql, ι Aql, κ Aql and λ Aql, were once part of the now-obsolete constellation Antinous.^[21]

References

^ ^a ^b ^c ^d ^e ^f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
^ ^a ^b ^c ^d Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars, 8: 59, Bibcode:1984SAAOC...8...59C
^ ^a ^b Cowley, Anne; Fraquelli, Dorothy (February 1974), "MK Spectral Types for Some Bright F Stars", Publications of the Astronomical Society of the Pacific, 86 (509): 70, Bibcode:1974PASP...86...70C, doi:10.1086/129562
^ ^a ^b ^c ^d ^e ^f ^g Fuhrmann, Klaus (February 2008), "Nearby stars of the Galactic disc and halo - IV", Monthly Notices of the Royal Astronomical Society, 384 (1): 173–224, Bibcode:2008MNRAS.384..173F, doi:10.1111/j.1365-2966.2007.12671.x
^ ^a ^b Mantegazza, L.; Poretti, E. (June 2005), "Projected rotational velocities of some Delta Scuti and Gamma Doradus stars", Communications in Asteroseismology, 146: 37–39, Bibcode:2005CoAst.146...37M, doi:10.1553/cia146s37
^ ^a ^b Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), "The Revision of the General Catalogue of Radial Velocities", Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E
^ Reiners, Ansgar (January 2006), "Rotation- and temperature-dependence of stellar latitudinal differential rotation", Astronomy and Astrophysics, 446 (1): 267–277, arXiv:astro-ph/0509399, Bibcode:2006A&A...446..267R, doi:10.1051/0004-6361:20053911, S2CID 8642707
^ ^a ^b Kamper, Karl W.; Legget, David; McCarthy, Donald W. Jr. (August 1989), "Astrometric-spectroscopic binary star orbits. III - Alpha Ophiuchi and Delta Aquilae", Astronomical Journal, 98: 686–691, Bibcode:1989AJ.....98..686K, doi:10.1086/115169
^ ^a ^b ^c ^d Baines, Ellyn K.; Blomquist, Solvay; Clark III, James H.; Gorney, Jim; Maier, Erin; Sanborn, Jason; Schmitt, Henrique R.; Stone, Jordan M.; van Belle, Gerard T.; Braun, Kaspar von (2023-01-09). "Simultaneous Six-way Observations from the Navy Precision Optical Interferometer". The Astronomical Journal. 165 (2): 41. Bibcode:2023AJ....165...41B. doi:10.3847/1538-3881/aca277. ISSN 0004-6256.
^ ^a ^b Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247, S2CID 118362423
^ ^a ^b Schröder, C.; Reiners, Ansgar; Schmitt, Jürgen H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo", Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377
^ "del Aql -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-06
^ Bailer-Jones, C. A. L. (March 2015), "Close encounters of the stellar kind", Astronomy & Astrophysics, 575: 13, arXiv:1412.3648, Bibcode:2015A&A...575A..35B, doi:10.1051/0004-6361/201425221, S2CID 59039482, A35.
^ ^a ^b Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 61. ISBN 0-486-21079-0. Retrieved 2010-12-12.
^ Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology, retrieved 2012-02-06
^ Kaler, Jim. "Delta Aql". Retrieved 2017-03-10.
^ Bečvář, A. (1951). Atlas Coeli Skalnaté Pleso II - Katalog 1950.0. Přírodovědecké Vydavatelstrí. p. 277. Retrieved 10 March 2017.
^ Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429
^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived September 29, 2009, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
^ Ian Ridpath's Star Tales - Antinous